1. Field of the Invention
The present invention relates to a composite filter used for a communication apparatus such as a portable phone terminal, an antenna duplexer, and a communication apparatus.
2. Related Art of the Invention
A filter is usually used for a communication apparatus such as a portable phone terminal. There is a multi-input/single-output filter, which receives a plurality of signals and outputs one signal, as one of such filters.
FIG. 7 shows the structure of a portable phone terminal 60. A conventional multi-input/single-output filter like this is used for the portable phone terminal 60. The portable phone terminal 60 is a dual band terminal, which can perform radiocommunication, by using either of two frequency bands of a 1.5-GHz frequency band and an 800-MHz band.
FIG. 2 shows the frequency composition of the 800-MHz band that the portable phone terminal 60 uses.
A D band 23 and a D band 28 are frequency bands used in a communication system where the portable phone terminal 60 performs transmission and reception simultaneously. The D band 23 is a band used for reception in the portable phone terminal 60, and the D band 28 is a band used for transmission in the portable phone terminal 60.
An A-band 25 and an A-band 27 are frequency bands used in a communication system different from the above-described system. The A-band 25 is a band used for reception in a portable phone terminal, and the A-band 27 is a band used for transmission in the portable phone terminal. The communication system that uses the A-band 25 and A-band 27 is a communication system not performing the simultaneous transmission and reception. A C band 24 and a C band 26 are frequency bands used in a communication system the same as the above-described communication system. The C band 24 is a band used for reception in the portable phone terminal 60, and the C band 26 is a band used for transmission in the portable phone terminal 60. The communication system that uses the C band 24 and C band 26 is a communication system not performing the simultaneous transmission and reception the same as the above. The portable phone terminal 60 can use each communication system corresponding to the D band, A-band, or C band by switching the bands according to a region such as a country where the portable phone terminal 60 is used. Specifically, a communication system that uses the D band is, for example, a PDC full duplex system. A communication system that uses the A-band is, for example, a usual timesharing PDC system, and a communication system that uses the C band is also, for example, a usual timesharing PDC system. In addition, it is needless to say that any communication system besides this is sufficient so long as the communication system that uses the D band is a communication system performing the transmission and reception simultaneously and the communication system that uses the A-band and C band is a communication system not performing the transmission and reception simultaneously.
The portable phone terminal 60 comprises a transmitting circuit section 1, a receiving circuit section 2, a base band section 3, a switch 4, an antenna 5, an antenna 6, a 1.5-GHz band SAW filter 17, and, a composite filter 33.
The base band section 3 is a circuit that modulates a base band signal, outputs the modulated signal as an intermediate frequency signal to the transmitting circuit section 1, and demodulates the intermediate frequency signal inputted from the receiving circuit section 2 to output a sound signal. In addition, the base band section 3 contains a frequency converter that converts the base band signal into the intermediate frequency signal and converts the intermediate frequency signal into the base band signal.
The transmitting circuit section 1 is a circuit that outputs either a 1.5-MHz band transmitted-signal or an 800-MHz band transmitted-signal. In addition, the switching of which of the 1.5-GHz band transmitted signal and the 800-MHz band transmitted-signal are outputted is performed by a controlling circuit not shown.
The transmitting circuit section 1 comprises an upconverter 7a, a variable gain amplifier 81a, a filter 8a, a power amplifier 9a, a coupling capacitor 10, an isolator 11, a filter 12, an upconverter 7b, a variable gain amplifier 81b, a filter 8b, a power amplifier 9b, and a directional coupler 13.
The upconverter 7a is means of converting the intermediate frequency signal outputted from the base band section 3 into the 800-MHz band signal. The variable gain amplifier 81a is an amplifier whose gain is controlled by a controlling circuit not shown, and which amplifies the 800-MHz band signal, which is converted, in such a gain that the 800-MHz band signal may become a determined transmission power output. The filter 8a is a band-pass filter decreasing an unnecessary frequency component of the 800-MHz band signal outputted from the upconverter 7a. The power amplifier 9a is means of amplifying the signal outputted from filter 8a to a transmission output. The coupling capacitor 10 supplies a power monitor signal to adjust the output power of the power amplifier 9a. The isolator 11 passing the transmitted signal, outputted by the power amplifier 9a, to the filter 12, and interrupting the transmitted signal reflected from the filter 12. The filter 12 decreasing an unnecessary frequency component of the signal outputted from the isolator 11.
The upconverter 7b converts the intermediate frequency signal, outputted from the base band section 3, into a 1.5-GHz band signal. The variable gain amplifier 81b is an amplifier whose gain is controlled by a controlling circuit not shown, and which amplifies the 1.5-GHz band signal, which is converted, in such a gain that the 1.5-GHz band signal may become a determined transmission power output. The filter 8b decreases an unnecessary frequency component of the 1.5-GHz band signal outputted from the upconverter 7b. The power amplifier 9b amplifies the signal outputted from the filter 8b to a transmission output. The directional coupler 13 passes the signal, outputted from the power amplifier 9b, to the switch 4 and not passing a reflected wave from the switch 4 to the power amplifier 9b, and supplies a power monitor signal to a controlling circuit that adjusts the output power of the power amplifier 9b and is not shown.
The receiving circuit section 2 converts the signal, inputted from the composite filter 33, into the intermediate frequency signal to output the signal to the base band section 3.
The receiving circuit section 2 comprises a low-noise amplifier 19a, a filter 20a, a mixer 21a, a low-noise amplifier 19b, a filter 20b, a mixer 21b, and a filter 22.
The low-noise amplifier 19a amplifies the 800-MHz band signal received. The filter 20a decreases an unnecessary frequency component of the signal amplified by the low-noise amplifier 19a. The mixer 21a is a signal, which passed the filter 20a, into the intermediate frequency signal.
The low-noise amplifier 19b amplifies the 1.5-GHz band signal received. The filter 20b decreases an unnecessary frequency component of the signal amplified by the low-noise amplifier 19b. The mixer 21b converts a signal, which passed the filter 20b, into the intermediate frequency signal.
Moreover, the filter 22 decreases an unnecessary frequency component included in the signal converted into the intermediate frequency.
The 1.5-GHz-band-receiving SAW filter 17 is a surface acoustic wave filter that passes the 1.5-GHz band signal received, and attenuates a signal except the 1.5-GHz band that is used for reception.
The composite filter 33 is a multi-input/single-output filter having a plurality of inputs and one output.
The composite filter 33 comprises a dielectric filter 30, an A-band-receiving SAW filter 31, and a switch 32.
The dielectric filter 30 is a dielectric coaxial filter that passes a signal in the D band 23, and attenuates a signal in the D band 28.
The A-band-receiving SAW filter 31 is a surface acoustic wave filter that passes a signal in the A-band 25.
The switch 32 switches which of an output of the A-band-receiving SAW filter 31. And output of the dielectric filter 30 is outputted to the receiving circuit section 2, and matching impedance with the receiving circuit section 2.
The switch 4 switches inputs of the composite filter 33 which receives a signal received by the antennas 5 and 6, and switches outputs of the transmitting circuit section 1 is inputted into the antennas 5 and 6.
The operation at the time of the portable phone terminal 60 communicating by a communication system using the D band 23 and D band 28 will be explained.
In this case, the portable phone terminal 60 performs simultaneous transmission and reception that the portable phone terminal 60 transmits a transmitted wave and receives a received wave at the same time.
That is, the intermediate frequency signal outputted from the base band section 3 is inputted into the upconverter 7a of the transmitting circuit section 1. The upconverter 7a converts the inputted intermediate frequency signal into a transmission frequency signal, that is, a signal at a frequency included in the D band 28. This transmission frequency signal is amplified in such a gain that the transmission frequency signal may become a transmission output determined by the variable gain amplifier 81a, is decreased by the filter 8a for its unnecessary frequency component, and is amplified to a transmission output by the power amplifier 9a. The amplified signal passes the isolator 11, is decreased by the filter 12 for a strain component, and is inputted to the switch 4. The switch 4 is switched so that an output signal of the filter 12 may be inputted into the antenna 5 or 6. Hence, the signal outputted from the filter 12 is inputted into the antenna 5 or antenna 6, and is radiated as an electric wave from the antenna 5 or antenna 6 in the air.
On the other hand, at the same time as the above-described transmitting operation, the electric wave transmitted from a base station is converted into an electrical signal by the antenna 5 or antenna 6, and is outputted into the switch 4. The switch 4 switches under the control of a controlling circuit, not shown, which of the 1.5-GHz band SAW filter 17, A-band-receiving SAW filter 31, and dielectric filter 30 receives the electrical signal outputted from the antenna 5 or antenna 6. Now, since this system communicates by the communication system using the D band 23 and D band 28, the switch 4 is switched so that this electrical signal may be outputted as a received signal to the dielectric filter 30. Hence, the received signal is outputted to the dielectric filter 30.
Moreover, since simultaneous transmission and reception are performed, the transmitted signal outputted from the transmitting circuit section 1 is outputted to the antennas 5 and 6 via the switch 4 and is radiated in the air, and simultaneously, a part of the transmitted signal is inputted from the switch 4 to the dielectric filter 30. This transmitted signal is high-power in comparison with the received signal. Hence, the dielectric filter 30 that is strong in a large amount of power is used instead of a SAW filter as a filter for the D band 23. The dielectric filter 30 attenuates the transmitted signal included in the D band 28, and passes the received signal included in the D band 23.
The switch 32 is switched by a controlling circuit, not shown, so as to output an output signal from the dielectric filter 33 to the low-noise amplifier 19a. The switch 32 selectively switches an output signal from the dielectric filter 30, and makes the output signal inputted into the low-noise amplifier 19a. 
The low-noise amplifier 19a amplifies the signal inputted from the switch 32. The amplified signal is decreased as an unnecessary frequency component by the filter 20a, and is converted into an intermediate frequency signal by the mixer 21a. The filter 22 decreases an unnecessary frequency component included in the signal converted into the intermediate frequency to output the signal to the base band section 3.
Next, the operation at the time of the portable phone terminal 60 communicating by a communication system using the A-band 25 and A-band 27 will be explained.
In this case, when the portable phone terminal 60 outputs a transmitted wave, the receiving circuit 2 does not output the intermediate frequency signal to the base band section 3. That is, the receiving operation is stopped. Then, when the receiving circuit 2 inputs the received signal and converts the signal into an intermediate frequency signal to output the signal to the base band section 3, the transmitting circuit 1 does not output the transmitted signal. In this manner, the portable phone terminal 60 switches the transmitting and receiving operation in time-sharing.
That is, when the transmitting operation is performed, the transmitting circuit section 1 outputs the transmitted signal to the switch 4 similarly to the case of the above-mentioned D band. The switch 4 is switched under the control of a controlling circuit, not shown, so that the inputted signal may be inputted to the antenna 5 or antenna 6. Hence, the signal inputted from the transmitting circuit section 1 to the switch 4 is radiated from the antenna 5 or antenna 6 as an electric wave in the air.
Moreover, at the time of receiving operation, the switch 4 is switched by a controlling circuit, not shown, so that a received signal converted into an electrical signal by the antenna 5 or antenna 6 may be inputted into the A-band-receiving SAW filter 15. Hence, the received signal that is converted into the electrical signal by the antenna 5 or antenna 6 is inputted into the A-band-receiving SAW filter 31 through the switch 4. In this case, since the transmitting circuit section 1 stops its operation, that is, does not output a transmitted signal, the transmitted signal is not inputted into the A-band-receiving SAW filter 31. The A-band-receiving SAW filter 31 passes a received signal in the A-band 25, and attenuates a signal, having a frequency except the A-band 25, as a noise component.
Moreover, the switch 32 is selectively switched by the controlling circuit, not shown, so that a signal outputted from the A-band-receiving SAW filter 31 may be inputted into the low-noise amplifier 19a. Hence, the signal having passed the A-band-receiving SAW filter 31 is inputted into the low-noise amplifier 19a. At this time, the switch 32 matches an output impedance of the A-band-receiving SAW filter 31 with an input impedance of the low-noise amplifier 19a. 
The signal inputted into the low-noise amplifier 19a is converted into an intermediate frequency signal by the receiving circuit section 2 similarly to the case of the communication system that uses the D band 23 and D band 28, and is outputted to the base band section 3.
Next, the operation of the case that the portable phone terminal 60 communicates by the communication system that uses the 1.5-GHz band will be explained.
In this case, similarly to the communication system that uses the A-band 25 and A-band 27, the portable phone terminal 60 switches the transmitting and receiving operation in time-sharing.
At the time of transmission, the intermediate frequency signal outputted from the base band section 3 is inputted into the upconverter 7b of the transmitting circuit section 1, and is converted into a transmission frequency signal in the 1.5-GHz band by the upconverter 7b. The signal outputted from the upconverter 7b is amplified in such a gain that the signal may become a transmission output determined by the variable gain amplifier 81b, is decreased by the filter 8b for its unnecessary frequency component, is amplified to a transmission output by the power amplifier 9b, and is outputted to the switch 4 through the directional coupler 13.
The switch 4 is switched under the control of a controlling circuit, not shown, so that the output from the directional coupler 13 may be inputted into the antenna 5 or antenna 6. Hence, the transmitted signal outputted from the directional coupler 13 is inputted into the antenna 5 or antenna 6 through the switch 4, and is radiated as an electric wave from the antenna 5 or antenna 6 in the air.
In addition, at the time of reception, the received signal that is converted into the electrical signal by the antenna 5 or antenna 6 is inputted into the switch 4. The switch 4 is switched by a controlling circuit not shown so that the received signal received by the antenna 5 or antenna 6 may be inputted into the 1.5-GHz band SAW filter 17. Hence, the received signal that is outputted from the antenna 5 or antenna 6 is inputted into the 1.5-MHz band SAW filter through the switch 4. The 1.5-GHz band SAW filter 17 outputs the received signal to the low-noise amplifier 19b of the receiving circuit section 2 with decreasing an unnecessary frequency component. The low-noise amplifier 19b amplifies the inputted signal, the amplified signal that is inputted into the mixer 21b with being decreased for its unnecessary frequency component by the filter 20b. The mixer 21b converts the inputted signal into an intermediate frequency signal, and after being decreased by the filter 22 for its unnecessary frequency component, the intermediate frequency signal is outputted to the base band section 3.
In this manner, in regard to the composite filter 33, a dielectric filter that can endure also the high-power input is used as a filter for the D band 23 that performs simultaneous transmission and reception. In addition, a SAW filter with small size is used as a filter for the A-band 25 that does not perform simultaneous transmission and reception.
Moreover, a single-input/single-output filter is used also in another circuit portion of the portable phone terminal 60. As such a filter, it is possible to miniaturize the filter by using a SAW filter when a low-power signal is inputted, and a dielectric filter is used when a large attenuation is necessary.
Nevertheless, in general, a dielectric filter has a feature that an attenuation characteristic is not steep in the vicinity of a pass band in comparison with a SAW filter. Hence, though having a large attenuation in the D band 28, the dielectric filter 30 cannot have a large attenuation as much as expected in the A-band 25 whose frequency is more adjacent to the D band 23.
Hence, if a signal, formed by directly connecting an output of the A-band-receiving SAW filter 31 to an output of the dielectric filter 30 without the switch 32, is made an input into the low-noise amplifier 19, it is not possible to synthesize the outputs of the dielectric filter 30 and A-band-receiving SAW filter 31. That is, an output signal from the A-band-receiving SAW filter 31 passes from an output terminal of the dielectric filter 30 to an input terminal.
In this manner, since it is not possible to make the output impedance of the dielectric filter 30 infinite (open) in a frequency of a pass band of the A-band-receiving SAW filter 31, it is not possible to synthesize the outputs of the dielectric filter 30 and A-band-receiving SAW filter 31 if the switch 32 is not provided.
That is, in the conventional composite filter 33, so as to synthesize the outputs of the dielectric filter 30 and SAW filter 31, the switch 32 is needed.
In this manner, in the conventional composite filter 33, since it is necessary to use the switch 32 so as to synthesize the outputs, its size becomes larger for that. Moreover, the loss of the composite filter 33 becomes large due to the loss at the time of a signal passing the switch 33.
That is, a conventional composite filter has an problem that its size becomes large since it is necessary to use a switch for synthesizing outputs.
Moreover, the conventional composite filter has an issue that its loss becomes large since needing to use a switch so as to synthesize outputs.
In addition, as described above, the dielectric filter has an attenuation characteristic that is not steep in the vicinity of a pass band in comparison with a SAW filter. Hence, though the dielectric filter 33 can attenuate a high-power transmitted signal included in the D band 28, it involuntarily passes a noise component in the vicinity of the D band 23. Moreover, since the dielectric filter 33 needs to attenuate the high-power transmitted signal included in the D band 28 enough, it is necessary to use the dielectric filter 33 with a large attenuation. Therefore, the dielectric filter 33 is enlarged. Moreover, on the contrary, if the dielectric filter 33 that is small is used, an attenuation is insufficient, and hence, it becomes not possible to attenuate the high-power transmitted signal included in the d band 28 enough.
That is, a conventional composite filter has a problem in obtaining excellent filter characteristic with small in size and, in order to obtain excellent filter characteristics the composite filter is required to be large in size.
Moreover, there is a problem that, though an attenuation is large in size when an dielectric filter is used as a single-input/single-output filter, it is not possible to obtain a steep characteristic in the vicinity of a pass band.
Moreover, there is a problem that, though it is possible to obtain a steep attenuation characteristic in the vicinity of a pass band when a SAW filter is used as a single-input/single-output filter, it is not possible to obtain a large magnitude attenuation.
In consideration of the above-mentioned issues, the present invention aims at providing a composite filter, an antenna duplexer, and an communication apparatus that are small.
In addition, in consideration of the above-mentioned problems, the present invention aims at providing a composite filter, an antenna duplexer, and an communication apparatus that have low loss in a pass band.
Furthermore, in consideration of the above-mentioned problems, the present invention aims at providing a composite filter, an antenna duplexer, and an communication apparatus that each have a high attenuation in a pass band.
Moreover, in consideration of the above-mentioned problems, the present invention aims at providing a composite filter an attenuation of which is large even if a high-power signal is inputted, and which has a steep attenuation characteristic in the vicinity of a pass band.
In consideration of the above-mentioned problems, the present invention aims at providing a composite filter, an antenna duplexer, and an communication apparatus that each steeply attenuate a signal in the vicinity of a pass band and have a large attenuation.
One aspect of the present invention is a composite filter comprising:
a dielectric notch filter; and
a first surface acoustic wave filter, wherein an attenuation band of the dielectric notch filter and an attenuation band of the first surface acoustic wave filter have at least a common band portion; and
wherein the dielectric substance notch filter and the surface acoustic wave filter are connected cascade.
Another aspect of the present invention is the composite filter, wherein an attenuation frequency of the dielectric notch filter and an attenuation frequency of the first surface acoustic wave filter coincide substantially.
Still another aspect of the present invention is the composite filter, wherein an input signal is inputted into a terminal of the dielectric notch filter;
wherein another terminal of the dielectric notch filter is connected to a terminal of the first surface acoustic wave filter; and
wherein an output signal is outputted from another terminal of the first surface acoustic wave filter.
Yet still another aspect of the present invention is the composite filter, comprising:
a second surface acoustic wave filter one terminal of which receives an input signal, and another terminal of which is connected to another terminal of the first surface acoustic wave filter, wherein a terminal of the dielectric notch filter receives a signal in a first frequency band and a signal in a third frequency band that is a frequency band not including a common portion to the first frequency band;
wherein a terminal of the second surface acoustic wave filter receives a signal in a second frequency band that is a frequency band not having a common portion to the first frequency band and the third frequency band, and is a frequency band between the first frequency band and the third frequency band;
wherein both of a pass band of the dielectric notch filter and a pass band of the first surface acoustic wave filter include the first frequency band,
wherein a pass band of the second surface acoustic wave filter includes the second frequency band;
wherein both of an attenuation band of the dielectric notch filter and an attenuation band of the first surface acoustic wave filter include the third frequency band;
wherein a frequency interval between a frequency included in the first frequency band and a frequency included in the third frequency band is apart equally to or more than a predetermined frequency interval; and
wherein the first surface acoustic wave filter can block at least a signal in the second frequency band.
Still yet another aspect of the present invention is the composite filter, wherein the second surface acoustic wave filter can block at least a signal in the first frequency band.
A further aspect of the present invention is the composite filter, comprising:
at least a third filter one terminal of which receives an input signal, and another terminal of which is connected to another terminal of the first surface acoustic wave filter;
wherein a signal in frequency bands that do not have common portions to the first frequency band and the third frequency band and do not have common portions to each other is inputted into one terminal of the third surface acoustic wave filter;
Wherein a pass band of the third surface acoustic wave filter includes a frequency band including the signal inputted; and
wherein the third surface acoustic wave filter can block at least a signal in the first frequency band, a signal in the second frequency band, and a signal inputted to a third surface acoustic wave filter that is not itself.
A still further aspect of the present invention is the composite filter, wherein an attenuation frequency of the dielectric notch filter is adjusted so as to obtain an attenuation equal to or more than a predetermined amount by combining an attenuation of the dielectric notch filter with an attenuation of the first surface acoustic wave filter.
A yet further aspect of the present invention is the composite filter, wherein which of one terminal of the dielectric notch filter and the surface acoustic wave filter receives a signal is switched by a switch.
A still yet further aspect of the present invention is an antenna duplexer comprising:
the composite filter;
a transmission filter connected to the switch, wherein the first frequency band is a frequency band for reception when simultaneous transmission and reception is performed;
wherein the third frequency band is a frequency band for communication when the simultaneous transmission and reception is performed; and
wherein the switch not only electrically connects the antenna to one terminal of the dielectric notch filter, but also electrically connects an output of the transmission filter to the antenna when the simultaneous transmission and reception is performed.
An additional aspect of the present invention is a communication apparatus comprising:
the antenna duplexer;
a transmitting circuit outputting a transmitted signal to the transmission filter; and
a receiving circuit receiving a received signal outputted from the composite filter of the antenna duplexer.